Not only is Flinders to be regarded as a discoverer whose researches completed the world's knowledge of the last extensive region of the habitable globe remaining in his time to be revealed; not only as one whose work was marked by an unrivalled exactitude and fineness of observation; but also as one who did very much to advance the science of navigation in directions calculated to make seafaring safer, more certain, with better means and methods at disposal. Malte-Brun declared, when he died, that "the geographical and nautical sciences have lost in the person of Flinders one of their most brilliant ornaments,"[1] and that criticism, coming from a foreign critic than whom there was no better informed savant in Europe, was no mere piece of obituary rhetoric.

In 1805 he wrote a paper on the Marine Barometer, based upon observations made during his Australian voyages. The instrument employed was one which had been used by Cook; Flinders always kept it in his cabin. He was the first to discover, and this essay was the first attempt to show, the connection between the rise and fall of the barometer and the direction of the wind. Careful observation showed him that where his facts were collected the mercury of the barometer rose some time before a change from landbreeze to seabreeze, and fell before the change from seabreeze to landbreeze. Consequently a change of wind might generally be predicted from the barometer. The importance of these observations was at once recognised by men connected with navigation. As the Edinburgh Review wrote, dealing with Flinders' paper when presented before the Royal Society on March 27th, 1806:[2] "It is very easy for us, speculating in our closet upon the theory of winds and their connection with the temperature, to talk of drawing a general inference on this subject with confidence. But when the philosopher chances to be a seaman on a very dangerous coast, it will be admitted that the strength of this confidence is put to a test somewhat more severe; and we find nevertheless that Captain Flinders staked the safety of his ship and the existence of himself and his crew on the truth of the above proposition." Nowadays, indeed, the principal use of a barometer to a navigator aboard ship is to enable him to anticipate changes of wind.

Not less important were his experiments and writings upon variations of the compass aboard ship. The fact that the needle of a compass showed deviations on being moved from one part of a ship to another had been observed by navigators in the eighteenth century, but Flinders was the first to experiment systematically to ascertain the cause and to invent a remedy.[3]

He observed not only that the direction of the needle varied according to the part of the ship where it was placed, but also that a change in the direction of the ship's head made a difference. Further, he found that in northern latitudes (in the English Channel, for instance) the north end of the needle was attracted towards the bow of the ship; whilst in southern latitudes, in Bass Strait, there was an attraction towards the stern; and at the equator there was no deviation. He came to the conclusion that these results were due to the presence of iron in the ship. When he returned to England in 1810, he wrote a memorandum on the subject to the Admiralty, and requested that experiments might be made upon ships of the Navy, with the object of verifying a law which he had deduced from a long series of observations. His conclusion was that "the magnetism of the earth and the attraction forward in the ship must act upon the needle in the nature of a compound force, and that errors produced by the attraction should be proportionate to the sines of the angles between the ship's head and the magnetic meridian." Experiments were made at Sheerness, Portsmouth, and Plymouth on five vessels. He took a keen personal interest in them; and the result was his invention of the Flinders' bar, which is now used in every properly equipped ship in the world. The purpose of the bar, which is a vertical rod of soft iron, placed so that its upper end is level with or slightly above the compass needle, is to compensate for the effect of the vertical soft iron in the ship.[4] Flinders' work upon this technical subject was important even in the days of wooden ships. In this era of iron and steel ships it is regarded by every sailor as of the utmost value.

In Flinders' day the delicacy of the compass, its liability to error, the nature of the magnetic force to which it responds, and the necessity for care in its handling, were very little appreciated. "Among the nautical instruments taken to sea there are not any so constructed, nor of which so little care is taken afterwards, as the compass," he did not hesitate to write.[5]) Compasses were supplied to the Admiralty by contract, and were not inspected. They were stowed in storehouses without any regard to the attraction to which the needles might be exposed. They might be kept in store for a few years; and they were then sent on board ships without any re-touching, "for no magnets were kept in the dockyards, and probably no person there ever saw them used." When a compass was sent aboard a ship of the Navy, it was delivered into the charge of the boatswain and put into his store or sail-room. Perhaps it was put on a shelf with his knives and forks and a few marline-spikes. Flinders urged that spare compasses should be preserved carefully in officers' cabins. Magnets for re-touching were not kept in one ship in a hundred. Under these circumstances, he asked, "can it be a subject of surprise that the most experienced navigators are those who put the least confidence in the compass, or that ships running three or four days without an observation should be found in situations very different from what was expected, and some of them lost? The currents are easily blamed, and sometimes with reason. Ships coming home from the Baltic and finding themselves upon the shores of the Dutch coast, when they were thought to be on the English side, lay it to the currents; but the same currents, as I am informed, do not prevail when steering in the opposite direction." The last is a neat stroke of irony. Flinders strongly recommended that the Admiralty should appoint an inspector of compasses, that there should be at every dockyard an officer for re-touching compasses, and that a magnet for re-touching should be carried on each flagship. The recommendations may seem like a counsel of elementary precautions to-day, but they involved an important reform of method in 1810.

Flinders also wrote on the theory of the tides; a set of notes on the magnetism of the earth exists in manuscript; a manuscript of 106 pages, consisting of a treatise on spheric trigonometry, is illustrated by beautifully drawn diagrams, and includes an account of eight practical methods of calculating latitude and five of calculating longitude. In Mauritius he read all he could obtain about the history of the island, and wrote a set of notes on Grant's History.

He was eager to praise the work of previous navigators. Laperouse was especially a hero of his, and he wrote in French for the Société d'Émulation of Ile-de-France an account of the probable fate of that celebrated sailor. In an eloquent passage in this essay, speaking of the wreck, he cried: "O, Laperouse, my heart speaks to me of the agony that rent yours. Ah, your eyes beheld the hapless companions of your dangers and your glory fall one after another exhausted into the sea. Ah, your eyes saw the fruit of vast and useful labours lost to the world. I think of your sorrowing family. The picture is too painful for me to dwell upon it; but at least when all human hope abandoned you, then—the last blessing that God gives to the good—a ray of consolation shone upon your eyes, and showed you that beyond those furious waves which broke upon your vessels and swept away from you your companions another refuge was opened to your virtues by the angel of pity."

Knowing the extreme difficulties attaching to navigation, even when in the public interest he had to make a correction in the work of others, he was anxious to cause no irritation. He sent to the editor of the Naval Chronicle a correction in Horsburgh's Directions forSailing to and from the East Indies, but requested the editor to submit it first to the author of that work, and to suppress publication if Horsburg so desired. He never expressed a tinge of regret that he had chosen a field of professional employment wherein promotion and reward were not liberally bestowed. Entering the Navy under influential auspices, in a period when active service provided plentiful scope for advancement, he deliberately preferred the explorer's hard lot. The only prize money he ever won was £10 after Lord Howe's victory in 1794. "I chose a branch," he said in a letter to Banks, "which though less rewarded by rank and fortune is yet little less in celebrity. If adverse fortune does not oppose me, I will succeed." He succeeded beyond all he could have hoped.

The excellence of his charts was such that to this day the Admiralty charts for those portions of the Australian coast where he did original work bear upon them the honoured name of Matthew Flinders; and amongst the seamen who habitually traverse these coasts, no name, not even that of Cook, is so deeply esteemed as his. Flinders is not a tradition; the navigators of our own time count him a companion of the watch.